Some free-piston engines rely on position versus time control of pistons in which a desired position versus time trajectory of a piston is determined based on an initial position of the piston. As the system causes a piston to move, the control strategy measures how much the piston is deviating from the desired position versus time trajectory and attempts to compensate for any deviation in order to bring the piston closer to the desired position versus time trajectory. Some free-piston engines rely on control strategies that measure how much a piston is deviating from other suitable trajectories (e.g., position versus velocity) and attempt to compensate for any deviation in order to bring the piston closer to the desired trajectory.
These approaches typically rely on an open-form solution for controlling a piston's movement based on a previously determined trajectory and often do not take into account changing conditions in the engine, which would affect the movement of the piston. For example, after the desired trajectory is determined, conditions in the engine can change such that the desired trajectory is no longer applicable. Movement of the piston will still, however, be based on the original desired trajectory and deviation therefrom.
The figures are not intended to be exhaustive or to limit the disclosure to the precise form disclosed. It should be understood that the concepts and embodiments disclosed can be practiced with modification and alteration, and that the disclosure is limited only by the claims and the equivalents thereof.